Contrast expansion circuit arrangement



April 3, 1951 Filed Dec. 10, 1947 H.A.BROO5 INVENTOR AGENT Patented Apr. 3, 1951 CONTRAST EXPANSION CIRCUIT ARRANGEMENT Henricus Adrianus Broos, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application December 10, 1947, Serial No. 790,831 In the Netherlands September 13, 1946 This invention relates to a further improvement in the invention described and claimed in mycopending patent application, No. 661,520. In the .said parent application, a contrast expansion circuit arrangement is described in which use is made of a discharge tube comprising at least a cathode, a first control-grid,i a screen-grid, a second control-grid, a second screen-grid and an anode, the input voltage to be amplified being supplied to one or to either 4 Claims. (Cl. 179-171) of the two control-grids, whereas a control-voltage derived from the amplitude of the amplified. voltage (output voltage) is fed to the second i control-grid, the circuit of the first and the second screen-grids, which are electrically inter-., connected, including an impedance which is. so.

high for the freuuency of the oscillations to be. amplified that the slope of the characteristic curve indicating the anode current as a function of the input voltage is increased with increasing negative control-voltage.

Accordingto the present invention this cir- H cult-arrangement is im roved by providing 'a positive'feedback circuit between the anode and the first control-grid. The measure according to the present invention ensures plified than the circuit-arrangement according to the copending patent application.

In order that the invention maybe more clearly understood and readily carried into effect, it will vnowbe described more fully with reference to. the. accompanying drawing, in which ments' thereof.

Figs. l'fandi2'show, by way of example, embodi-' In Fig. 1, the input voltage to be amolifiedis' fed from the" terminals l and: to a first controlgrid 4 of a discharge tube 5. The amplified output voltage is abstracted from terminals 1 iiand- 8 through aresistance 6 included in the anode circuit. 'lfait'b'fthis'voltage is rectified with the use of a rectifying tube [5 and fed, as the control voltage, to a second control-grid H of the discharge" tube 5. v screen-grids l0 and- I2 includes a resistance ll of such high value that the slope of thecharacteristiccurve which shows the anode current considerablvgreater expansion of the input voltage to be am- I The circuit connected to two feedback circuit producing a positive feedback between the anode l4 and the first control-grid 4 of thetube 5; this feedback circuit may comprise, for example, a blocking condenser 30 and a potentiometer 3|, 32.

This may be appreciated as follows: owing to the resistance IT in the circuit of the grids II and I2 thevoltage of these grids is in phase opposition with the voltage of the first controlgrid 4. Set up between the screen-grid l0 and' the second control-grid H is thus a negative space charge which may be regarded as a virtual cathode. The part of the tube containing this virtual cathode, grid [2, and the anode operates as a pentode in which the anode current is controlled by thevoltage on thegrid I2, and the screen grid l0 can be considered 'as a space charge electrode. Thus the anode voltage is in phase opposition withthe voltage at the grid I2, that is tosay, it exhibits the same phase as the input voltage on the grid 4.

The provision of the circuit 30, 3|, 32 thus,

results in a positive feedback, so that the voltages on the grids 4, Ill and I2 are higher than would be the case without this feedback. The control voltage fed to the second control-grid ll controls the mutual conductance of the aforesaid pentode part of the tube 5. Since, however, I the control voltage on the grid l2 of this pentode part exhibits a higher value than without feedj back, 'a higher control voltage is set up and under '1 the influence thereofjth'e mutual'lconductance of, this tube part is subjected to a greater. variation? with the'result that :greaterfcontrast expansion; isobtained.

Fig.,2 of the drawing shows a similar circuit-' arrangement in which the input voltage is fed. tofth'e second control-grid I I. Also iri'this em I bodiment the provision of a feedback "circuit 30,

3t, 32 which brings about'a positive feedback results in considerable increase in contrast expan I sion of the input voltage.

What I claim is: 1, An amplifier circuit arrangement for expanding the amplitude of an electrical oscilla nr p i a e rqn .d e arge tube haw: ing a cathode, a first control grid, a first screen grid, a second control grid, a second screen grid and an anode, said tube having a characteristic wherein for a predetermined value of operating potential on said firstfland second screen grids relative to the potentials on the other elements of said tube the mutual conductance of the tube as represented by the anode current-control grid voltage ratio increases with an arithmetic decrease of the control voltage, means including a resistor common tosaid first and said second screen grids to apply operating potentials to said electron discharge tube, means to apply said oscillation to one of said control grids, means to" derive a control voltage proportional to the amplitude of said oscillation including a rectifying device having a cathode and having an anodecoupled to the anode of said tube, means intercoupling the cathode of said. rectifying device and the cathode of said tube and'..maintaining a substantially constant potential relationship therebetween, means to apply said voltage to said second control grid, said resistor having a resistance value at which the potential applied to said first and second screen grids is substantially equal to said predetermined value of operating potential, and network means intercoupling the anode of said discharge tube and the. first controlgrid-of said discharge tube in regenerative relationship at'the frequency of said oscillation.

2. An amplifier circuit arrangement for ex.- panding the amplitude of anelectrical oscillation, comprisingan electron discharge tube having a cathode, a first control grid, a first screen grid, a second controlgrid, a second screen grid and an: anode, said. tube. having a characteristic wherein for a predetermined value of operating potential on said first and second screen. grids relative to the potentials on. the-other elements of said tube the. mutual conductance of. the. tube as represented by the. anode currentecontrol grid. voltageratio increases. with. an. arithmetic decrease-of the control voltage, means including a resistor common to. said first and said second screen grids to'apply operating potentials to said.

electron discharge tube, means.to apply said oscillation to said first. control. grid, means to derive a control voltage proportional to the amplitude of. said oscillation. includingv a rectifying device having a cathode and having an anode coupled to. the anode of said.tube,.means intercoupling the cathode of said. rectifying device and the cathode of. said tube and maintaining a substantially constant potential relationship therebetween, means to apply said voltage to said secondcontrol grid,.saidresistor having a resistance value at which the potential applied to. said. first and. second screen. grids issubstantially. equal to. said predeterminedvalue of operating. potential,

and network means comprising a series circuit including a resistive element andv a capactive element intercoupling. the anode of said dischargetube and the first control grid of said discharge tube in'regenerative relationship at the frequency of said oscillation.

T3. 'Anamplifier circuit arrangement for expanding. the amplitude of an electrical oscillation, comprising an electron discharge tube having a .cathode, a first control grid, a first screen grid, a second control grid, a second screen grid and an anode, said tube having a characteristic wherein for a predetermined value of operating potential on said first and second screen grids relativto the potentials on the other elements of 'said' tube the mutual conductance of the tube as" represented by the anode current-control grid 4 voltage ratio increases with an arithmetic decrease of the control voltage, means including a resistor common to said first and said second screen grids to apply operating potentials to said electron discharge tube, means to apply said oscillation to said second control grid, means to derive a control voltageproportional to. the amplitude of said oscillation including a rectifying device having a cathode and having an anode coupled to the anode of said tube, means intercouplingthe cathode of said rectifying device and the cathode of said tube and maintaining a substantially constant potential relationship therebetween, means to apply said voltage to said second control grid, said resistor having a resistance value at which the potential applied to said first and second screen grids is substantially" equal to said predetermined value of operatingpotential, and network means comprising a series circuit including a resistive element and a capacitive element intercoupling the anodeof said discharge tube and the first control grid of said discharge tube in regenerative. relationship at the frequency of said oscillation.

4. An amplifier circuit arrangement for expanding the amplitude of an electrical oscillation, comprising an electron discharge: tube hav'- ing a cathode, a first. control grid, a first screen grid, a second control grid, a second screen grid .and an anode, said tube having a characteristic wherein for a predetermined value of operating potential on said first and second screen grids relative to the potentials on the other elements of said tube the mutual conductance of the tube'as represented by the anode currentrcontrol grid' voltage ratio increases with an arithmetic d'e crease of the control voltage, means including aresistor common to said first and said'seco'nd screen gric's to apply operating potentials to said electron; discharge tube, means to apply 'said oscillation to one of said control grids, means to" derive a control voltage proportional to the amplitude of said oscillation including a rectifying device having a cathode connected in common with the'cathode of said tube and having an anode coupled to the anode of said tube, means to apply said voltage to said second control grid, said resistor having a resistance value at which the potential applied to said first and second screen grids in substantially equal to said predetermined value of operating potential, and network means comprising'a series circuit including'a' resistive elementand a capacitiveeiement.

intercoupling the anode of-said discharge tube and the first control grid of said discharge'tube in regenerative relationship at the frequency of said oscillation.

Y HENRICUS ADRIANUS BROOS.

REFERENCES CITED The following references are of record in the file ofthis patent:

.UNITED STATES PATENTS Freeman,. vMan. 25,. 1941, 

